1. Field of the Invention
The present invention relates to a multi-channel rotary joint for allowing flow along separate routes without allowing a plurality of fluids of the same or different types to be mixed between relative rotational members in a CMP (Chemical Mechanical Polishing) apparatus (an apparatus for the surface polishing of semiconductor wafers) or the like.
2. Prior Art
For example, in the surface polishing of a semiconductor wafer with a CMP apparatus, a turntable and a top ring are individually rotated with the semiconductor wafer sandwiched in between them. The supply of a wafer polishing liquid, wafer pressurized air, wafer cleaning water (pure water), air-blowing air, or the like, or the suction discharge of polishing residue, the vacuum chucking of a semiconductor wafer and a lapping plate or the like, and so forth may be performed between the rotating member (the top ring or the turntable) and the stationary side that supports the rotating side (the CMP apparatus housing). In view of this, with a CMP apparatus, a rotary joint having a plurality of channels is generally provided in between the rotating member and the stationary member in order to allow a plurality of fluids of the same or different types to flow through individual routes (channels) between the relatively rotating members.
In one such multi-channel rotary joint provided between relatively rotating members and known in the past, a first joint structural member attached to the stationary member is rotatably linked to a second joint structural member attached to the rotating member, a plurality of mechanical seals aligned in the relative rotation axial direction are provided between the opposing peripheral surfaces of the first and second joint structural members, and a plurality of channels that pass through sealing regions formed between adjacent mechanical seals are provided for the first and second joint structural members (hereinafter the above multi-channel rotary joint will be referred to as a xe2x80x9cconventional jointxe2x80x9d).
However, the mechanical seals are structured so that a stationary seal ring fixed to one of the first and second joint structural members and a movable seal ring supported movably in the axial direction are rotated relative to each other while pressed into contact by a coil spring. Therefore, in addition to the installation space of the two seal rings, space is further required for the movement of the movable seal ring and for the installation of the coil spring. As a result, a large installation space is needed in the axial direction (the relative rotation axial direction of the first and second joint structural members).
Therefore, in the conventional joint in which a plurality of mechanical seals are lined up in the axial direction, the size in the axial direction is large; and the axial direction size increases along with the number of channels.
Also, the stationary seal ring and the movable seat ring must be in proper contact and vibration or axial runout between the first and second joint structural members must be effectively prevented in order for good sealing function to be realized with a mechanical seal. Therefore, the bearing that rotatably links the first and second joint structural members must be provided at least on both sides of the mechanical seal group, and leaving enough space for the installation of these bearings makes the rotary joint even larger in the axial direction. Naturally, as the number of mechanical seals increases, it eventually becomes impossible to effectively prevent axial runout and the like merely by disposing bearings on both sides of the mechanical seal group, making it necessary to dispose bearings in the middle part of the mechanical seal group as well.
Meanwhile, with a CMP apparatus or the like, even though there may be enough space in the direction (radial direction) perpendicular to the relative rotational axial direction of the two members due to the structure in which one relative rotational member (a rotating member such as a top ring) is rotatably supported on the other (a stationary member such as the CMP apparatus housing), it is often impossible to increase the size (of the space between the relative rotational members in which the rotary joint is disposed) beyond a certain point in the relative rotational axial direction.
Therefore, a conventional joint cannot be used for a CMP apparatus or the like that requires many fluid routes and that has limited space in the relative rotational axial direction. Even with a device without such space limitations, the overall device becomes larger than necessary when many fluid routes are required.
The size in the axial direction can be reduced with a conventional joint by way of using one of the mechanical seals as a means for sealing two channels. However, such a structure sometimes leads to leakage of fluid from one channel into the other due to pressure fluctuations within the channel and so forth. In such a case, even if the leak is very small, if the fluid flowing through the other channel is pure water for processing a wafer, for example, the admixture of the fluid flowing through the first channel can have adverse effects on the wafer. Therefore, in the conventional joint, when handling fluids that must not be admixed with fluids from another channel, there is no way to effectively reduce the size in the axial direction. Even if the mechanical seal is made to serve double duty as described above, the reduction in length is minimal.
Accordingly, it is an object of the present invention to provide a multi-channel rotary joint with which as many channels as possible can be provided with the same size in the axial direction as when a single channel is provided, which can be favorably installed in a small space, and with which a fluid that must not be admixed with other fluids can be made to flow efficiently.
It is another object of the present invention to provide a multi-channel rotary joint with which a plurality of fluids of the same or different types can flow efficiently between relative rotational members through independent channels without the fluids becoming mixed and without increasing the size in the axial direction.
It is a further object of the present invention to provide a multi-channel rotary joint with which even fluids that must not be mixed or brought into contact with other fluids, such as pure water for processing wafers, can be made to flow efficiently by providing a drain region between the sealing regions of adjacent channels.
It is yet another object of the present invention to provide an extremely functional and practical multi-channel rotary joint that can be used to advantage even in a CMP apparatus or the like that requires many fluid routes and has little space to install the rotary joint in the rotational axial direction between the relative rotational members.
The above objects are accomplished by a unique structure of the present invention for a multi-channel rotary joint that comprises:
a first joint structural member and a second joint structural member which are linked each other in a relatively rotatable fashion;
three or more sealing regions defined and formed by three or more mechanical seals which are lined up concentrically around a relative rotational axis, the sealing regions being provided between opposing end faces of the first and second joint structural members in a direction of a relative rotational axis of the joint structural members;
a drain region formed by at least one of the sealing regions;
a plurality of channels each independently passing through each of the sealing regions except for the sealing region that forms the drain region, the plurality of channels being provided in the first and second joint structural members; and
a drain path that opens into the drain region and is provided in one of the joint structural members.
The above-described sealing regions (including the one that forms or is used as the drain region) can be formed by annular regions between mechanical seals that are adjacent in the radial direction or can be formed by the inner peripheral region of the mechanical seal with the smallest diameter.
When the above multi-channel rotary joint is used for devices that require electrical connection between the relative rotational members, it is preferable that an electrical wire insertion path that passes through the inner peripheral region of the mechanical seal having the smallest diameter be provided in the first and second joint structural members. If this inner peripheral region is not used as part of the electrical wire insertion path, it can be used as a sealing region that constitutes part of the channel, or as the drain region.
In addition, in order to effectively prevent the admixture of bearing lubricating oil into the channel, along with further reducing the axial direction size and facilitating the maintenance of the bearing linking the first and second joint structural members, it is preferable to provide: a bearing which rotatably links opposing peripheral surfaces of the first and second joint structural members and is interposed between the first and second joint structural members, and an oil seal that is disposed between the bearing and an outer periphery of a mechanical seal that has a largest diameter, thus using an annular region between the mechanical seal and the oil seal as the drain region, and providing a drain path which opens into the drain region in one of the first and second joint structural members.